Heat exchanger

ABSTRACT

The invention relates to a plate heat exchanger ( 9 ) with a plurality of heat exchanger plates ( 1, 13 ), each comprising at least one section showing indentations ( 2, 3, 14, 15 ), intended to be placed against corresponding indentations ( 2, 3, 14, 15 ) of a heat exchanger plate ( 1, 13 ) of a corresponding design. The heat exchanger ( 9 ) has a first type of indentations ( 2, 14 ) and a second type of indentations ( 3, 15 ), wherein the number of said first type of indentations ( 2, 14 ) and said second type of indentations ( 3, 15 ) are differing.

CROSS REFERENCE TO RELATED APPLICATION

Applicant hereby claims foreign priority benefits under U.S.C. §119 fromDanish Patent Application No. PA 2010 01048 filed on Nov. 19, 2010, thecontents of which are incorporated by reference herein. Applicant alsocross-references this application to an application internal reference10 01 690 (Attorney Docket No. 6495-0508) filed on the same dayherewith, the contents of which are incorporated by reference herein.

TECHNICAL FIELD

The invention relates to a plate heat exchanger, comprising at least oneheat exchanger plate (preferably a plurality of heat exchanger plates)wherein at least one of said exchanger plates comprises at least onesection showing indentations, intended to be placed againstcorresponding indentations of a heat exchanger plate of a correspondingdesign. Furthermore, the invention relates to a heat exchanger plate,comprising at least one section showing indentations, intended to beplaced against corresponding indentations of a heat exchanger plate of acorresponding design.

BACKGROUND OF THE INVENTION

Modern heat exchangers of the plate heat exchanger type are oftenprovided with plates having a so-called herringbone pattern, i.e. apattern which has indentations consisting of straight ridges andvalleys. The ridges and valleys change their respective direction in thecentre, producing the pattern that resembles a herringbone. In a stackedheat exchanger pack, alternate plates are turned by 180° so that theindentations cross one another. The thus stacked heat exchanger platesare brazed together, thus forming a compact and mechanically stable heatexchanger pack. Using the herringbone pattern of the heat exchangerplates, the resulting heat exchanger pack comprises a pattern of fluidchannels through which the respective two fluids can flow and exchangetheir thermal energy.

When a heat exchanger pack of the afore-described type is exposed topressure (in particular fluid pressure) and heat, the plates distort,causing a bending moment in the plates. In order to withstand highpressures, relatively thick metal sheets are used, e.g. with a thicknessof 0.4 mm.

When such metal plates are pressed into the herringbone pattern, anunfavourable material flow takes place. If the press tool is not veryaccurately manufactured, cracks can appear in the plates. The relativelythick plates also require a high pressure in the press tool.

In a fully brazed heat exchanger, the joints are typically brazed withcopper or a copper alloy solder placed between the plates. The copper(alloy) solder is frequently introduced as a coating of the metalsheets. The solder material collects at the crossing points of theindentations. The surface area and strength of the solderings aretherefore quite small.

A fluid which is made to flow through a heat exchanger with aherringbone pattern is forced to flow over the ridges and down into thevalleys. There are no unbroken straight flow-lines. At the leading edgeof the ridges the flow rate is high, whereas the flow rate of the fluidis low behind the ridges (i.e. in the valleys). This variation in flowrate is very large. In the heat exchanger the heat transfer rate is highwhere the flow rate is high, but the heat transfer rate is low where theflow rate is low. A smaller variation in flow rate as it is the case inheat exchangers with a herringbone pattern is hence favourable.

When the flowing fluid contains two phases, i.e. the fluid is a mixtureof a gas and a liquid, the recurring changes of direction at the ridgesand valleys will have the effect that the gas forces the liquid awayfrom contact with the plates. This reduction in wetting of the heatexchanger plates' surfaces also reduces the heat transfer rate.

The shape of the channels through a heat exchanger of the herringbonedesign also gives rise to a high pressure drop in the fluid as it passesthrough the heat exchanger. This pressure drop is proportional to thework done in forcing the fluid through the heat exchanger. A highpressure drop thus means high (mechanical) power consumption.

A heat exchanger trying to solve at least some of these problems isknown from the document US 2007/0261829 A1. In this document it issuggested to provide a pattern on a heat exchanger plate that comprisesindentations in the form of bulges and hollows, and between whichchannels are formed, passing through the heat exchanger. The shape ofthe thus formed channels gives rise to a moderate variation in flow ratethrough the heat exchanger, thereby resulting in a higher heat transferrate. The thus formed heat exchanger plates are stacked together in away that an upper plate is turned so that its downward-pointing hollows(bottoms) abut against the upward-pointing tops of a lower plate. Theupper and lower plates are brazed together by forming solderings wherethe heat exchanger plates touch each other. However, it has been found,that these plates are prone to break in the side walls of the bulgesduring operation of the heat exchanger. Obviously, this seriouslyadversely affects the lifetime of the heat exchanger.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a plate heatexchanger that has improved characteristics over plate heat exchangers,known in the state of the art. It is another object of the presentinvention to provide a heat exchanger plate, in particular a heatexchanger plate for building a plate heat exchanger that has improvedcharacteristics over heat exchanger plates, known in the state of theart.

It is suggested to design a plate heat exchanger, comprising at leastone heat exchanger plate, preferably a plurality of heat exchangerplates, wherein at least one of said heat exchanger plates comprises atleast one section showing indentations and wherein said indentations areintended to be placed against corresponding indentations of a heatexchanger plate of a corresponding design in a way that at least a firsttype of indentations and at least a second type of indentations areprovided, wherein the number of said first type of indentations and saidsecond type of indentations are differing. The expression “number ofindentations” can be understood in a broad way. In particular, the“different number of indentations” can relate to the overall number ofthe respective indentations on the respective heat exchanger plateand/or to a certain part of the heat exchanger plate's surface. In somerespect, the different number of indentations can thus be seen as adensity of indentations, expressed as, for example, the number of therespective type of indentations per unit area. As already mentioned, the“number of indentations” can relate to only a certain part of the heatexchanger plate, wherein the “part” usually has to have a certain size,in particular has to be chosen in a way that summing up and averagingthe number of indentations per unit area will lead to a more or lessstable number, if the size of the area is changed by a certain amount.In particular, it is possible to choose a somewhat advantageous surfacepart of the heat exchanger plate when looking for the number (and/or thedensity) of indentations. For example, it is not unusual for a heatexchanger plates to deviate from a “standard pattern” in the vicinity ofthe fluid inlet and/or the fluid outlet. If such “non-standard” areasare not considered, the respective numbers will usually improve inquality. The “different number” can be essentially any deviation from aratio of one. In particular, the ratio can be ≧1.05, ≧1.1, ≧1.2, ≧1.3,≧1.4, ≧1.5, ≧1.6, ≧1.6, ≧1.75, ≧2, ≧2.25, ≧2.5, ≧2.75, ≧3, ≧3.25, ≧3.5,≧3.75, ≧4, ≧4.25, ≧4.5, ≧4.75 and/or ≧5. Preferentially, a naturalnumber is chosen for the ratio. Of course, the reciprocals of thesuggested values can be used as well. When it comes to distinguishingthe first type of indentations from the second type of indentations (andpresumably even a third, fourth, fifth or even more different types ofindentations), essentially every possibility on how to distinguish thosetypes can be encompassed. For example, the types can be distinguished bysize, surface area, shape (for example parallel to the heat exchangerplate's surface and/or perpendicular to the heat exchanger plate'ssurface), material, surface coating, surface treatment, heat exchangerplate's thickness at or near the indentation's position, direction ofthe indentation (for example upward and/or downward and/or tilted),angular positioning of the respective indentation and so on.Combinations of two or more of the mentioned features are possible aswell, of course. Furthermore, when talking about an “indentation”, thisdoes not necessarily mean that the respective section of the heatexchanger plate has been actively shaped. Instead, it is also possiblethat an indentation has been formed by actively shaping (for example bypressing or the like) of areas, being close to the respectiveindentation. Furthermore, the expression “indentation” can be understoodin a very broad way, as well. As an example, an indentation can be aprotrusion, a recess, a groove, a bulge, a hollow, a land, a web or thelike. As it is usual with heat exchanger plates for plate heatexchangers, two plates, neighbouring each other, can be of analternating, corresponding design. In other words, it is possible that aplate heat exchanger mainly consists of two differently arranged heatexchanger plates, having a corresponding design of indentations (whereinan indentation, going upward will contact a corresponding indentationfrom the corresponding heat exchanger plate that is going downward.Although it is in principle possible that two differently designed heatexchanger plates (or even more) are manufactured for building such aplate heat exchanger, for example, normally only a single heat exchangerplate is designed and manufactured, wherein the aforementioned twodifferent “designs” of heat exchanger plates are achieved by turningevery second plate in the stack of heat exchanger plates by 180°. Ofcourse, the uppermost, as well as the lowermost plate has usually adifferent design for effectively closing the heat exchanger block.Typically essentially flat metal sheets can be used for this. After thestack of heat exchanger plates (and possibly other components) has beenput together, the “raw” plate heat exchanger arrangement will usually besent through a tunnel furnace to braze/solder the respective componentstogether, to form a compact and mechanically stable block. Of course, itis possible that the plate heat exchanger will (essentially) show onlythe aforementioned two different types of indentations. However, it isalso possible that a third, a fourth, a fifth or even more differenttypes of indentations are provided as well. The presently suggestedplate heat exchanger has to have (like any heat exchanger) two separatesets of fluid channels that are fluidly separated from each other. Thisis, because the thermal energy has to be transferred from one fluid tothe other. In rare cases, more fluids, and hence more separated fluidchannels, are used within a single heat exchanger. Usually, the two (oreven more) fluids show different characteristics. For example, the twodifferent fluids can have a different state of matter (for example, onefluid is a liquid, while another fluid is a gas). Also, one or bothfluids can be a mixture of a gas and a liquid, with a varying gas toliquid ratio. Furthermore, the two different fluids will normally have adifferent temperature (at least at the entrance port of the stack typeheat exchanger) and/or a different pressure. Even more, the differentfluids can have a different viscosity, a different density, a differentthermal capacity and so on. By using a different number (density) fordifferent types of indentations, it is very easy to provide a mechanicalstability that is different for the two different fluid channels,containing the two different fluids. This way, the mechanical stabilityof the plate heat exchanger can remain at the same level or can be evenincreased, while the overall dimension of the stack type heat exchangercan be reduced. For example, if the first type of indentations is“responsible” for the connection with the “upper” heat exchanger plate,while the second type of indentations is “responsible” for theconnection with the “lower” heat exchanger plate, by choosing adifferent number of first and second type of indentations, themechanical stability between the “middle” and “upper” plate on the onehand and between the “middle” and “lower” plate on the other hand can beadapted to the fluid pressure of the respective fluid, flowing in therespective channels, that is to be expected. Furthermore, using theproposed design, it is very easy to generate two different types offluid channels for the two different fluids. As an example, the twodifferent fluid channels can differ in cross section (in particularshape and/or size), the curvature of the respective fluid channel, thenumber of “obstacles” (that are generating vortices, for example) and/orin different ways. This way, an advantageous heat exchanger can beachieved. For example, the overall size of the resulting heat exchangerand/or the lifetime of the resulting heat exchanger and/or the resultingheat exchanger's effectiveness can be enhanced.

In particular, it is possible that the plate heat exchanger is designedin a way that said first type of indentations and said second type ofindentations are of a different design and/or of a different size. Usingsuch a design, it is particularly simple to provide different strengthof the respective connections (for example to take into accountdifferent pressures of the respective fluids) and/or to adapt the sizesand/or the characteristics of the fluid channels, being formed betweenthe respective connections, to the particular necessities of therespective fluid. The expression “different design” can be understood ina broad way. The “different design” cannot only relate to the sizeand/or the shape of the respective indentation (especially when lookingfrom above and/or from below onto the respective heat exchanger plate).For example, the different design (in particular the size and/or theshape) can relate to a cross-sectional view onto the respectivestructure, as well. Furthermore, even more different “designs” can beencompassed by this suggestion, for example a different thickness of therespective heat exchanger plate in the respective section, a differentmaterial, a different material coating, a different surface treatmentand/or the like.

It can prove to be advantageous, if the plate heat exchanger is designedin a way that said first type of indentations and said second type ofindentations are of a different shape. The “shape” of the respectiveindentation can be in particular the shape, when seen from above and/orfrom below onto the respective heat exchanger plate. Using a differentshape for the different types of indentations can be particularly usefulif by choosing a different shape, the respective connections and/or theresulting fluid channels are particularly well suited for thecharacteristics of the respective fluid involved. As an example, byusing a first shape for the first type of indentations, a very low fluidresistance can be achieved for the first fluid, used within the heatexchanger. By using a different shape for the second type ofindentations, however, a higher fluid resistance can be achieved for thesecond fluid involved. Such a higher fluid resistance is introducingadditional turbulence. Such additional turbulence can increase thepossible heat transfer rate from the respective fluid to the channelwall and finally to the other fluid, thus utilising the higherresistance for increased heat transfer, thus increasing the performanceof the resulting heat exchanger. In particular if a third, fourth (oreven more) type of indentations is present, a mixture of “same shapes”and “different shapes” can prove to be useful, as well. Also, it ispossible to realise combination effects by choosing an appropriatecombination of number of indentations and shape of indentations.

However, it can also be of advantage, if the plate heat exchanger isdesigned in a way that said first type of indentations and said secondtype of indentations show essentially the same shape. Using the sameshape can be particularly advantageous, if the respective shape hascertain (advantageous) characteristics, for example a particularly lowfluid resistance, a particularly high mechanical strength, aparticularly advantageous ratio of surface area to the length of thesurrounding edge or the like.

In particular, it is possible to design the plate heat exchanger in away that at least said first type of indentations and/or at least saidsecond type of indentations show at least partially an elliptical shape,a circular shape, a teardrop-like shape, a polygonal shape and/or asymmetric polygonal shape. These shapes have proven to be particularlyadvantageous during first experiments. In particular, an ellipticalshape and/or a circular shape usually result in a particularly highmechanical strength, a particular long lifetime of the resultingconnection and/or a particularly large connection area, when compared tothe bordering line of this connection area, combined with the relativelylow fluid flow resistance. A teardrop-like shape will usually result ina particularly low fluid flow resistance, thus reducing mechanicalenergy losses. A polygonal shape and/or a symmetric polygonal shape willusually result in an introduction of (slight to moderate) additionalturbulence, which can improve the heat transfer efficiency. By asymmetric polygonal shape, usually a shape is meant, in which themajority or even all of the sides of the polygon show essentially thesame length.

Another preferred embodiment of a plate heat exchanger can be achievedif the number and/or the arrangement of at least said first type ofindentations and/or at least said second type of indentationscorresponds to the shape of at least said first type of indentationsand/or at least said second type of indentations. By using suchsymmetries, a particularly strong heat exchanger with a long lifetimecan be achieved, because mechanical stresses that are occurring aredistributed comparatively homogeneously. Furthermore, using suchsymmetries, usually the resulting fluid flow patterns are advantageous,such decreasing fluid flow resistance and/or increasing heat transferperformance.

Another preferred design of the plate heat exchanger can be achieved ifat least said first type of indentations and/or at least said secondtype of indentations are designed, at least in part, with an essentiallyflat top and/or bottom surface area. Having such a flat surface area,the strength of the resulting connection with the correspondingindentation of the neighbouring heat exchanger plate can be particularlystrong, while soldering material (for example copper solder and/orcopper alloy solder) can be saved.

Yet another preferred embodiment of the plate heat exchanger can beachieved if at least said first type of indentations and/or at leastsaid second type of indentations are arranged, at least in part, alongstraight lines, wherein said straight lines are preferably arranged atan angle relative to a side edge of the corresponding heat exchangerplate. Using such an arrangement for the indentations, a simple, yetvery efficient design of the heat exchanger plates can be achieved. Inparticular, it is possible that for building a complete plate heatexchanger, essentially only a single type of indented heat exchangerplate has to be used, whereas every second plate in the stack of heatexchanger plates is turned by 180° with respect to the respectiveneighbouring heat exchanger plates. This way, manufacturing tools andstorage room can be saved, thus lowering production cost. The straightlines are preferably arranged at an angle of approximately 45° withrespect to the corresponding side edge of the corresponding heatexchanger plate. However, certain variations around this preferred angleare possible. For example, the interval of possible angles can start at30°, 35°, 40°, 42°, 43° and/or 44° and end at 46°, 47°, 48°, 50°, 55°and/or 60°. But the present invention in its broadest embodiment is notlimited to any such angle.

Yet another preferred embodiment of a plate heat exchanger can beachieved if at least said first type of indentations and/or at leastsaid second type of indentations are arranged, at least in part, in sucha way that at least sectionally at least one of the circulating fluidshas to follow a curved fluid path. This way, it is usually possible toincrease the heat transfer rate of the respective fluid, thus increasingthe performance of the heat exchanger.

Additionally or alternatively it is possible to design the plate heatexchanger in a way that at least said first type of indentations and/orat least said second type of indentations are arranged, at least inpart, in such a way that at least sectionally at least one straightconduit for at least one of the circulating fluids is formed. By thisdesign, the fluid flow resistivity can usually be decreased. This way,mechanical energy can be saved. This design is particularly useful withfluids, showing a particularly high and/or low viscosity and/or incombination with a design of the plate heat exchanger in whichturbulence is generated by different means.

Furthermore it is suggested to design the plate heat exchanger in a waythat at least said first type of indentations and/or at least saidsecond type of indentations are arranged, at least in part, in such away that at least sectionally at least one conduit for at least one ofthe circulating fluids is arranged in parallel to at least one of theside edges of the corresponding heat exchanger plate. This way, usuallya particularly advantageous fluid flow between the fluid inlet duct andthe fluid outlet duct of the respective fluid channel can be achieved.

Another particularly preferred embodiment of the plate heat exchangercan be achieved if at least one of said heat exchanger plates is formed,at least partially, of a metal plate and/or a metal alloy plate, whereinsaid plate preferably comprises, at least sectionally, a coating madeout of an adhesive material, preferably made out of a solderingmaterial. The metal plate can be, for example, made out of aluminum, analuminum alloy, iron, copper, an iron alloy (for example steel), acopper alloy or the like. As an adhesive material, it is possible that aglue or the like is used. Of course, it is also possible that asoldering material (or brazing material) like copper or a copper alloyis used. It is to be noted that this suggested feature may be prosecutedin connection with the preamble of originally filed claim 1.

Furthermore, it is suggested that a heat exchanger plate, comprising atleast one section showing indentations, that are intended to be placedagainst corresponding indentations of a heat exchanger plate of acorresponding design, is designed in a way that at least a first type ofindentations and at least a second type of indentations are provided,wherein the number of said first type of indentations and said secondtype of indentations are differing. Such a heat exchanger plate isparticularly useful for manufacturing a plate heat exchanger of theabove described type. Furthermore, the suggested heat exchanger platecan show the same features and advantages, as already described inconnection with the stack type heat exchanger, at least in analogy.Furthermore, the heat exchanger plate can be modified in theaforementioned sense, at least in analogy.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will become more apparent, whenlooking at the following description of possible embodiments of theinvention, which will be described with reference to the accompanyingfigures, which are showing:

FIG. 1: a first embodiment of a heat exchanger plate for a plate heatexchanger in a schematic view from above;

FIG. 2: the heat exchanger plate of FIG. 1 in a schematic view from theside;

FIG. 3: a plurality of heat exchanger plates according to the embodimentof FIGS. 1 and 2, stacked together, in a schematic view from the side;

FIG. 4: a typical embodiment of a plate heat exchanger in a schematicperspective view;

FIG. 5: a second embodiment of a heat exchanger plate for a plate heatexchanger in a schematic view from above;

FIG. 6: the heat exchanger plate of FIG. 5 in a schematic view from theside;

FIG. 7: a plurality of heat exchanger plates according to the embodimentof FIGS. 5 and 6, stacked together, in a schematic view from the side;and

FIG. 8: typical flow paths for the fluids within a plate heat exchangerusing heat exchanger plates according to the embodiment of FIGS. 5 to 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Plate heat exchangers (9), such as the typical embodiment, shown in FIG.4, are well-known devices for the transfer of heat between two differentfluids. Plate heat exchangers (9) are used in many differentapplications, for example in the automotive industry, for cooling andheating of buildings and so on.

A plate heat exchanger (9) comprises a plurality of heat exchangerplates (1, 13) that are stacked over each other. The individual heatexchanger plates (1, 13) are designed with a pattern of indentations (2,3, 14, 15), typically designed as bulges and hollows and/or as ridgesand valleys (the latter one in particular in combination with theherringbone design). On the very top and the very bottom of the plateheat exchanger (9), flat metal sheets (16) are provided for retainingthe fluids within the plate heat exchanger (9). Furthermore, connections(11, 12) for inlet (11) and outlet (12) of two fluids are provided aswell.

The stack of heat exchanger plates (1, 13) is usually manufactured byloosely arranging the heat exchanger plates (1, 13) over each other andjoining them together by soldering to form a mechanically stableintegral unit.

Because of the pattern of indentations (2, 3, 14, 15) on the heatexchanger plates (1, 13), separate channels for the two fluids, areformed by the soldering process, wherein the separate channels arefluidly separated from each other. Typically, the two fluids circulatein a counterflow between alternate pairs of heat exchanger plates (1,13). This technology as such is generally known.

FIG. 1 is a plan view onto a first possible embodiment of a heatexchanger plate (1), showing a distinct pattern of indentations (2, 3).As can be seen from FIG. 1, the depicted heat exchanger plate (1) isprovided with a pattern of first bulges (2) and second bulges (3), andnot with the currently widely used herringbone pattern. Furthermore,circular ports (17) are provided near the four corners of the heatexchanger plate (1). These circular ports (17) are the typicalconnections for the inlet (11) and outlet (12) of two different fluidsinto and out of the plate heat exchanger (9). Within the heat exchangerplate (1), shown in FIG. 1, a square is drawn with a dashed line. Therespective surface part of the heat exchanger plate (1) is shown on theright side of FIG. 1 at an enlarged scale. Thanks to the enlarged scale,the pattern of first bulges (2) and second bulges (3) of the heatexchanger plate (1) is clearly visible. Both first bulges (2) and secondbulges (3) are raised by a given height relative to a reference plate(18) in opposite directions. The flanks of the bulges (2, 3) have anedge angle of approximately 45 degrees. This deformation can be easilydone by pressing techniques. In contrast to the herringbone pattern, thepattern of bulges (2, 3) of the present heat exchanger plate (1) is wellsuited to the pressing process, since the necessary deformation of theplate sheets is comparatively small. This way, the risk of cracksappearing in the heat exchanger plate (1) can be significantly reduced.

The first bulges (2) and second bulges (3) constitute a first patternconsisting of the first bulges (2), and a second pattern consisting ofthe second bulges (3). In the present embodiment of a heat exchangerplate (1), first bulges (2) and second bulges (3) have substantiallyflat first tops (4) and flat second tops (5) with a corresponding firstsurface area and second surface area, respectively. As can be seen fromFIG. 1, the surface area of each individual first top (4) of the firstbulges (2) is smaller as compared to the surface area of each individualsecond top (5) of the second bulges (3). Since the number of firstbulges (2) and second bulges (3) is essentially the same, the overallsurface area of the first tops (4) of the first bulges (2) is likewisesmaller as compared to the overall surface area of the second tops (5)of the second bulges (3).

When a heat exchanger (9) is made from a plurality of heat exchangerplates (1), the heat exchanger plates (1) are connected such that e.g.the first surface areas (4) of one plate (1) are fixedly connected(soldered, brazed, glued) to the first surface areas (4) of a lowerplate (1), and in the same manner, the second surface areas (5) of theone plate (1) are fixedly collected (soldered, brazed, glued) to thesecond surface areas (5) of an upper plate (1) (see, for example, FIG.3). Due to the comparatively large surface areas of the first surfaceareas (4) and the second surface areas (5), relatively strongconnections are made in the present embodiment. The connections bymaterial engagement (10) are indicated in FIG. 3 between twoneighbouring first surface areas (4) and two neighbouring second surfaceareas (5), respectively. The connection by material engagement (10) canbe established by any process known in the art, such as brazing,soldering, glueing etc.

In operation, the heat exchanger (9) is filled with pressurised fluids(wherein the pressure of the two fluids involved can differ) which tendsto force the heat exchanger plates (1) apart. The heat exchanger plates(1) can also expand due to increased temperatures, introduced by thefluids. Because of the pattern of first and second bulges (2, 3), allstresses generated in the plate material are directed essentially in thedirection of the plate's material, and hence no or only small bendingmoments are created. The absence of such bending moments increases thestrength and the lifetime of the structure. The strength of the heatexchanger (9) is also increased by the comparatively large contactingareas (10) between the first and second bulges (2, 3). Because of thisimproved strength, thinner sheet metal can be used for the heatexchanger plates (1). Alternatively, the sheet metal with the usualthickness of 0.4 mm can be used, giving the heat exchanger (9) abursting pressure of 600 bar compared with 200 bar for a standard heatexchanger with a herringbone pattern and the same metal sheet thickness.

FIG. 2 shows a profile view of the first (2) and second (3) bulges alonglines A and B, represented by a dashed and solid line, respectively.

The heat exchanger (9) according to the present invention also offersthe possibility that the opposite sides may be adapted to differentpressures of the fluids as it may often be desired.

By shaping the first (2) and second (3) bulges in way that they havedifferent surface areas (first (4) and second (5) surface area), it isfirst of all possible that the flow characteristics (which have aninfluence on the pressure drops of the fluids) can be made different atthe two sides of each of the plates (1) and hence can be made differentfor the two fluids involved. Furthermore, due to the different size thecontact zones (4, 5) of two adjacent plates (1) (where the contact zones(4, 5) are connected by material engagement (10)) it is possible todesign the final heat exchanger (9) in a way that it can have a higherpressure resistance towards one fluid, as compared towards the otherfluid.

Therefore it is possible to design the resulting heat exchangers (9)according to the specific requirements. In particular, the sizes (bothabsolute and relative) and distributions of the first (2) and second (3)bulges may be designed in such a way that specific flow rates and/orpressure drops can be obtained. At the same time the contact zones (4,5) of the heat exchanger plates (1) can be dimensioned according to therequired strength.

In the illustrated first embodiment, the surface areas of both the firstbulges (2) and the second bulges (3) show an oval shape with theelongated diameter (i.e. the main axis of the ellipse) pointingsubstantially in the direction of the fluid flow. This way, thecross-section in the direction of the fluid flow is minimised and hencethe fluid flow resistance of the fluid (and consequently the pressureloss in the fluid) can be reduced.

First experiments indicate that forming the flat tops (4) and (5) withan elliptical shape is superior to forming them with circular shapes.There is some indication that circular shapes are prone to cracks in theside walls of the first (2) and/or second (3) bulges. While the strengthof the connection by material engagement (10) between neighbouring heatexchanger plates (1) depends highly on the surface areas of the flattops (4) and (5), the load capacity of the walls depends strongly on thecircumferential length and the thickness of the plate sheet. If thethickness of the plates were to be changed in order to obtain a similarstrength of the walls and the connections (10), the heat exchangingeffectiveness of the heat exchanger (9) would be adversely affected.Using an elliptic shape for the first (2) and/or the second (3) bulgesthe circumferential length can be easily increased with constant platesheet thickness and/or surface area of the connections (10).

As a matter of completeness, it should be mentioned that according toalternative embodiments any other suitable shape for the first (2)and/or the second (3) bulges is possible as well. In particular, byusing different shapes, it is likewise possible to increase thecircumferential lengths without increasing the surface area of theconnections (10).

In FIG. 3 a plurality of heat exchanger plates (1) that are connected toeach other using connections by material engagement (10) are shown in aview from the side. The direction of the view is parallel to the lines Aand B of FIG. 1. It can be seen that channels (6, 7) with two differentcross-sections are formed. The larger channels (6) are formed by theheat exchanger plates (1) between the first bulges (2) with the firsttops (4), showing the smaller surface areas. Of course, the connectionsbetween the (smaller) first tops (4) will yield a weaker connection ascompared to the connections between the (larger) second tops (5).Furthermore, between the second bulges (3), smaller second channels (7)are formed. However, these smaller second channels (7) are suitable forhigher pressurised fluid due to the stronger mechanical connections (10)between the (larger) second tops (5).

According to the embodiment of the heat exchanger plate (1) that isshown in FIGS. 1 to 3, first (2) and second (3) bulges are placedsymmetrically in a rectangular grid, with first (2) and second (3)bulges on every other grid point. Thus, they are located alternatingeach other along a number of parallel lines, the distance between first(2) and second (3) bulges being equal and the distance between suchparallel lines being equal. The channels (6, 7) that are formed for thefluids will then follow an essentially zig-zag line. In other words, therespective fluid is not forced to flow over ridges and valleys as in theherringbone pattern. Instead, it will only encounter the rounded,“pillar-like” constrictions (in form of first (2) and second (3) bulges)at the connecting points (10) between the stacked heat exchanger plates(9).

Naturally, first (2) and second (3) bulges will still cause a certainamount of variation in fluid flow rate and direction and some turbulencein the fluid. However, it is known that it is usually not desirable toeliminate turbulence completely, because usually laminar fluid flowgives poorer heat transfer rate. With the proposed pattern of bulges (2,3) slight to moderate fluid flow rate variation in the fluid isobtained. Thus a lower pressure drop across the heat exchanger (9) perheat transfer unit is obtained for a given average fluid flow rate ofthe fluid. The mechanical power required to force a fluid through theheat exchanger (9) per heat transfer unit is therefore also lowered, inparticular when compared to a heat exchanger with a herringbone pattern.

For improved fluid flow characteristics, the first (4) and second (5)flat top areas are presently positioned such that their longestdiameters (main axis of the ellipse) substantially extend in a directionparallel to the direction of fluid flow in the heat exchanger (9). Thedirection of flow in the heat exchanger may be defined as the local mainflow direction of the fluid, when averaged over a plurality of bulges(2, 3).

However, they could also be positioned with their longest diameterarranged with any angle relative to the direction of fluid flow in theheat exchanger (9), and may even show varying angles over the surface ofthe heat exchanger plates (1). Also, the sizes and/or shapes of thefirst top (4) and/or second top (5) areas may change over the surface ofthe heat exchanger plate (1), thus changing individual and/or relativeflow and pressure characteristics locally.

A particular relevant embodiment for this is if the angles of thelongest diameters are changing from substantially perpendicular toparallel relative to the direct connecting line between fluid inlet (11)and fluid outlet (12). Such an arrangement will assist the fluidsentering through the fluid inlet (11) in distributing over the wholewidth of the heat exchanger plates (1), and again, will assist thefluids coming from the sides of the heat exchanger plates (1) to bedirected to the fluid outlet (12).

As shown in FIG. 3, first (6) and second (7) channels, especially therespective centres of first (6) and second (7) channels, have a gap (8)with a straight, essentially undisturbed fluid flow path.

When looking at a second channel (7), for example, the fluid does notneed to change its direction because of the proximity to the upper firsttops (4). Still, the fluid is affected to some extent by the proximityof the left and right second tops (5). If a heat exchanger (9) withchannels (7) of this type is used with a two-phased fluid, i.e. a fluidthat is a mixture of both gas and liquid, the gas phase tends to flowalong said gap (8) in the centre of the second channel (7). This meansthat the gas can flow through the heat exchanger (9) withoutcompromising the wetting of the walls of the heat exchanger plates (1)by the liquid phase of the fluid. This provides better heat transfer.The same applies to the first channels (6) in analogy.

In some operational cases, nuclear boiling can also occur instead ofsurface evaporation along the walls of the heat exchanger plates (1).Such nuclear boiling will occur especially in hollows, where the fluidflow rate is significantly reduced. Such nuclear boiling will furtherimprove the heat transfer rate.

In an alternative embodiment (not shown), the first (2) and second (3)bulges are located symmetrically in a grid, but unlike the embodiment ofa heat exchanger plate (1) as shown in FIGS. 1 to 3, the grid isarranged so that the channels (6, 7) formed are parallel with the edgesof the heat exchanger plate (1). This arrangement usually results in alower pressure drop but also a lower heat transfer rate, because thetops (4, 5) obscure one another.

However, the arrangement can be modified in essentially any way. Inparticular, the pattern does not need to be symmetrical over the wholeplate. This way, different arrangements can be used to direct the flowof fluid in the desired way and to control turbulence and pressure drop.

Furthermore, it is not necessary that the pattern of first (2) andsecond (3) bulges (and presumably even more different types of bulges;not shown) covers essentially the whole of the heat exchanger plate (1).The pattern can be combined with deflecting barriers and baffles, withcompletely flat surfaces, and also with conventional herringbonepatterns if this is required for whatever reason.

FIG. 5 is a plan view of a second possible embodiment of a heatexchanger plate (13). Such a heat exchanger plate (13) can be used formanufacturing plate heat exchanger (9), as shown in FIG. 4. The presentsecond embodiment is somewhat similar to the first embodiment of a heatexchanger plate (1), as shown in FIGS. 1 to 3. However, the arrangement,number and shape of the first (14) and second bulges (15) are different.

In the presently shown second embodiment of a heat exchanger plate (13),the first bulges (14) have an essentially hexagonal shape, while thesecond bulges (15) have an essentially triangular shape. Similar to thefirst embodiment of the exchanger plate (1), both first (14) and second(15) bulges of the presently shown heat exchanger plate (13) have firsttops (19) and second tops (20) with an essentially flat top surface,respectively. It can be seen from FIG. 5 that the surface area of asingle first top (20) (first bulge (15)) is larger than the surface areaof a single second top (19) (second bulge (14)).

The arrangement of the first (14) and second (15) bulges relative toeach other is chosen to reflect the individual shapes of the first (14)and second (15) bulges. Since the first bulges (14) are shaped in formof a hexagon, the second bulges (15) are likewise arranged in ahexagonal formation (22) around a central first bulge (14). Therefore,there are six second bulges (15) arranged around each first bulge (14).Similarly, since the second bulges (15) are shaped in form of atriangle, the first bulges (14) are arranged in a triangular formation(21) around a central second bulge (15). Therefore, there are threefirst bulges (14) arranged around each second bulge (15).

In the presently shown embodiment, the arrangement of first (14) andsecond (15) bulges is done in a way that a corner of the hexagonallyshaped first bulge (14) is pointing towards a triangularly shaped secondbulge (15). Contrary to this, a straight line of the triangularly shapedsecond bulge (15) is “pointing” towards a hexagonally shaped first bulge(14). To achieve this arrangement, the second bulges (15) are positionedin a way that the second bulges (15) change direction along a line (C),as seen in FIG. 5. First experiments have shown that this particulararrangement reduces mechanical stresses in the metal sheet of the heatexchanger plate (13) when at least one of the fluids is changingpressure and/or temperature. Therefore, the lifetime of the resultingheat exchanger (9) can usually be enhanced. Furthermore, the suggestedarrangement of first (14) and second (15) bulges have shown acomparatively good heat transfer rate with relatively low mechanicalenergy losses (pressure drop of the fluids) in first experiments.

However, a different arrangement of first (14) and second (15) bulgesand/or a different alignment of first (14) and second (15) bulges can beadvantageous with different fluids and/or fluid characteristics. Inparticular, by choosing an appropriate arrangement and/or alignment offirst (14) and second (15) bulges, the resulting heat exchanger (9),manufactured from the presently suggested heat exchanger plates (13) canbe adapted to the actual requirements.

FIG. 6 shows a profile view of the first (14) and second (15) bulgesalong lines (C) and (D), represented by a dashed and a non-broken line,respectively. By introducing a different number and/or shape and/or sizeof first (14) and second (15) bulges, different flow and/or pressurecharacteristics can be obtained on the opposite sides of a heatexchanger plate (13). This is due to the different number, shape andsize of the “obstacles”, seen by the fluid on its way through the heatexchanger (9).

It shall be noted, that the figure is highly illustrative showing theprofiles as straight lines, this typically will not be the case. Theillustrated ‘straight’ lines usually will be curved, and the profilewill in real life typically comprise no ‘corners’.

In FIG. 7, an arrangement of several heat exchanger plates (13) that arestacked over each other and connected to each other by means of materialengagement (23) are shown. The depicted view is onto the side of such astack of heat exchanger plates (13). The direction of the view is chosento be parallel to the lines (C) and (D) of FIG. 5. Hence FIG. 7 isillustrating “two levels” of a heat exchanger (9). It can be seen fromFIG. 7 that, according to the presently described second embodiment, thelarger first channels (24) are located between the less numerous secondbulges (15). Likewise, the smaller second channels (25) are locatedbetween the first bulges (14) that are larger in number than the secondbulges (15).

It should be noted that the overall strength of the connection betweentwo heat exchanger plates (13) is not only determined by the surfacearea of the first tops (19) and/or second tops (20) of the first bulges(14) and the second bulges (15), respectively, but also by the(relative) number of first bulges (14) and/or second bulges (15).Therefore, it is possible to obtain a higher strength of the overallconnection between two neighboring heat exchanger plates (13) throughthe (smaller) second flat tops (20) in comparison to the overallconnection through the first flat tops (15), simply by increasing thenumber of second flat tops (20). Of course, the overall connectionstrength through the first flat tops (15) can be increased by thismethod as well.

By such an adaption of the overall mechanical connection strength, it ispossible to optimise the resulting heat exchanger (9) with respect tothe maximum fluid pressures and/or the maximum fluid temperaturesoccurring in the specific design. This way, it is usually possible tooptimize the heat exchanger's effectivity, the size of the resultingheat exchanger (9) and to lower the manufacturing costs.

As it has been described in connection with the first embodiment of aheat exchanger plate (1) shown in FIGS. 1 to 3, designing first bulges(14) and/or second bulges (15) with a shape, being different from thecircular shape (in the presently shown example triangular and hexagonalshapes are used), it is possible to elongate the circumferential lengthof the edge lines of the flat tops (19, 20), without increasing the sizeof the respective surface area. As already described, this will resultin a design that is less prone to mechanical failure due to pressuredifferences and/or temperature differences. Therefore, the lifetime ofthe resulting heat exchanger (9) can usually be increased.

Even with respect to the presently shown second embodiment of a heatexchanger plate (13), it is possible that any other suitable shape,number and/or size can be used for the first bulges (14) and/or thesecond bulges (15).

Similar to the already described first embodiment of a heat exchangerplate (1), in the presently suggested second embodiment of a heatexchanger plate (13) the first channels (24) and second channels (25)may gaps (26) with a straight, essentially undisturbed fluid flow, alsocalled ‘lines of sight’. If such ‘lines of sight’ exists and theirextension will be highly depending on the exact designs of the heatexchanger plate (1) with first (14) and second (15) bulges, such astheir relative distance in relation to the extension and size of theirflat tops (19, 20). Similar ‘lines of sight’ may exist in the embodimentof e.g. FIG. 3. Here, when looking at the first channel (24), the fluiddoes not need to change direction because of the proximity to the firsttops (19), but is affected only to some extent by the second tops (20).(And likewise when looking at the second channel (25).) If a heatexchanger (9) with channels (24, 25) of this type is used with atwo-phased fluid, the gas phase tends to flow along said gap (26) in thecentre of the first channel (24) or second channel (25). Therefore, thegas phase flows through the heat exchanger (9) without compromising thewetting of the heat exchanger plates (13) by the liquid phase. Thisprovides better heat transfer.

Of course, even with respect to the second embodiment of a heatexchanger plate (13) (or even in connection with different designs of aheat exchanger plates), in some operational cases nuclear boiling canoccur instead of surface evaporation, especially in hollows, where thefluid flow rate is significantly lowered. This can further improve theheat transfer rate.

A further aspect of the suggested heat exchanger plates (1, 13), inparticular with respect to the second embodiment of a heat exchangerplate (13) is that flow characteristics will be highly different inrelation to the direction of fluid flow relative to the pattern of firstbulges (2, 14) and the second bulges (3, 15).

FIG. 8A shows the paths (27 a, 28 a) defined in the overall direction offluid flow, where the dashed curvy line (28 a) illustrates a fluid flowpath on the side of the heat exchanger plate (13) defined by the firstbulges (14) (which are seen as protrusions, while the second bulges (14)are seen as hollows). The unbroken curvy line (27 a) illustrates in thesame manner a fluid flow path seen on the other side of the heatexchanger plate (13) that is defined by the second bulges (15). Bothflow paths (27 a) and (28 a) are repeatedly changing their respectivedirection of fluid flow (similar to some form of a zig-zag) due todeflection at the first bulges (14) and the second bulges (15) along theheat exchanger plate (13), respectively.

In a fluid flow direction orthogonal to the overall direction of fluidflow the fluid flow will not see the same obstructions in that the firstand second bulges (14, 15) are arranged nicely along lines (C) and (D)(see FIG. 5), thus leaving undisturbed ‘higways’ (27 b) and (28 b) offluid flow paths for the fluid flows, being substantially withoutobstructions (see FIG. 8B). At least, the paths (27 b) and (28 b) may besuch that their resistance to flow is lower than in other flowdirections.

Such undisturbed ‘higways’ (27 b, 28 b) have the benefit of a betterdistribution of the fluid flow over the heat exchanger plate (13) (andtherefore over the completed heat exchanger (9)), so that the flowresistance will be lower in a fluid flow direction orthogonal to theoverall direction of fluid flow (the overall direction of fluid flowcorresponds to the direction of fluid flow parallel to the “long” sidesof the heat exchanger plate (13)). By having a lower fluid flowresistance in a direction, being different from the direction leadingfrom an inlet (11) to an outlet (12), the fluid will be betterdistributed over the heat exchanger plate (13) as a whole.

Other modifications, previously described with respect to the firstembodiment of a heat exchanger plate (1), can also be employed for thepresently described second embodiment of a heat exchanger plate (13) (orany other modification of a heat exchanger plate), at least in analogy.

Additional information can be taken from the application, filed by thesame applicant at the same patent office on the same day under theinternal reference number 10 01 690 (Attorney Docket No. 6495-0508). Thecontents of this other application is incorporated by reference into thepresent application.

While the present invention has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisinvention may be made without departing from the spirit and scope of thepresent.

1. A plate heat exchanger, comprising at least one heat exchanger plate,preferably a plurality of heat exchanger plates, wherein at least one ofsaid exchanger plates comprises at least one section showingindentations, intended to be placed against corresponding indentationsof a heat exchanger plate of a corresponding design, wherein at least afirst type of indentations and at least a second type of indentations,wherein the number of said first type of indentations and said secondtype of indentations are differing.
 2. The plate heat exchangeraccording to claim 1, wherein said first type of indentations and saidsecond type of indentations are of a different design and/or of adifferent size.
 3. The plate heat exchanger according to claim 1,wherein said first type of indentations and said second type ofindentations are of a different shape.
 4. The plate heat exchangeraccording to claim 1, wherein said first type of indentations and saidsecond type of indentations show essentially the same shape.
 5. Theplate heat exchanger according to claim 1, wherein at least said firsttype of indentations and/or at least said second type of indentationsshow at least partially an elliptical shape, a circular shape, ateardrop-like shape, a polygonal shape and/or a symmetric polygonalshape.
 6. The plate heat exchanger according to wherein the numberand/or the arrangement of at least said first type of indentationsand/or at least said second type of indentations corresponds to theshape of at least said first type of indentations and/or at least saidsecond type of indentations.
 7. The plate heat exchanger according toclaim 1, wherein at least said first type of indentations and/or atleast said second type of indentations are designed, at least in part,with an essentially flat top and/or bottom surface area.
 8. The plateheat exchanger according to claim 1, wherein at least said first type ofindentations and/or at least said second type of indentations arearranged, at least in part, along straight lines (A, B, C, D), whereinsaid lines (A, B, C, D) are preferably arranged with an angle relativeto a side edge of the corresponding heat exchanger plate.
 9. The plateheat exchanger according to claim 1, wherein at least said first type ofindentations and/or at least said second type of indentations arearranged, at least in part, in such a way, that at least sectionally atleast one of the circulating fluids has to follow a curved fluid path.10. The plate heat exchanger according to claim 1, wherein at least saidfirst type of indentations and/or at least said second type ofindentations are arranged, at least in part, in such a way, that atleast sectionally at least one straight conduit for at least one of thecirculating fluids is formed.
 11. The plate heat exchanger according toclaim 1, wherein at least said first type of indentations and/or atleast said second type of indentations are arranged, at least in part,in such a way that at least sectionally at least one conduit for atleast one of the circulating fluids is arranged in parallel to at leastone of the side edges of the corresponding heat exchanger plate.
 12. Theplate heat exchanger according to claim 1, wherein at least one of saidheat exchanger plates is formed, at least partially, of a metal plateand/or a metal alloy plate, wherein said plate preferably comprises, atleast sectionally, a coating made out of an adhesive material,preferably made out of a soldering material.
 13. A heat exchanger platecomprising at least one section showing indentations, intended to beplaced against corresponding indentations of a heat exchanger plate of acorresponding design, wherein at least a first type of indentations andat least a second type of indentations, wherein said first type ofindentations and said second type of indentations, wherein the number ofsaid first type of indentations and said second type of indentations arediffering.
 14. The plate heat exchanger according to claim 9, wherein atleast said first type of indentations and/or at least said second typeof indentations are arranged, at least in part, in such a way that atleast sectionally at least one conduit for at least one of thecirculating fluids is arranged in parallel to at least one of the sideedges of the corresponding heat exchanger plate.